Integrated circuits require metallizations to connect the various individual devices within the integrated circuit. As both the complexity and the number of devices in the integrated circuits increase, the dimensions of the lines forming the interconnections, i.e., metallizations, generally decrease as does the spacing between the lines. Although there are often problems associated with the integrity of the lines, these problems become still more severe in very large scale integration (VLSI) due to the very small dimensions of the lines.
Aluminum is frequently the preferred metallization because of its relatively low resistivity and its compatibility with doped silicon. There is the potential for at least four problems to arise from the use of the aluminum. First, aluminum is not a very hard metal and it is possible to scratch the metal before it has been passivated. Second, electromigration of atoms within the lines is possible. Electromigration potentially leads to electrical discontinuities in the line. This problem can be alleviated, and perhaps solved, by depositing the aluminum is a bamboo type structure which stops the electromigration. See U.S. Pat. No. 4,438,450 issued on Mar. 20, 1984. Third, for many applications, it is desirable to deposit the metallization over discontinuities or steps in the physical surface while retaining electrical continuity. This is often difficult to realize with conventional deposition techniques. Fourth, the aluminum lines may develop either or both lateral or vertical hillocks. The development of hillocks is undesirable because it may make further fabrication steps difficult because the lines no longer have their desired geometry.
Several approaches in addition to that already mentioned have been tried in attempts to solve some or all of these problems. For example, films of materials such as Ti, TiSi.sub.2, TaSi.sub.2, have been deposited over aluminum films in attempts to suppress hillock formation. Additionally, ion implantation with heavier ions such as As, Kr, and Xn has been used for the same purpose. While the approaches are perfectly adequate in eliminating vertical hillock growth, they do not eliminate the problems caused by hillocks growing horizontally from the side of the aluminum metallization. This problem is especially severe with finely spaced Al line. Nor do they necessarily address the other problems discussed.